Reciprocal space slicing: A time-efficient approach to femtosecond x-ray diffraction

Abstract

An experimental technique that allows faster assessment of out-of-plane strain dynamics of thin film heterostructures via x-ray diffraction is presented. In contrast to conventional high-speed reciprocal space-mapping setups, our approach reduces the measurement time drastically due to a fixed measurement geometry with a position-sensitive detector. This means that neither the incident (ω) nor the exit (2θ) diffraction angle is scanned during the strain assessment via x-ray diffraction. Shifts of diffraction peaks on the fixed x-ray area detector originate from an out-of-plane strain within the sample. Quantitative strain assessment requires the determination of a factor relating the observed shift to the change in the reciprocal lattice vector. The factor depends only on the widths of the peak along certain directions in reciprocal space, the diffraction angle of the studied reflection, and the resolution of the instrumental setup. We provide a full theoretical explanation and exemplify the concept with picosecond strain dynamics of a thin layer of NbO2.

Emission of coherent THz magnons in an antiferromagnetic insulator triggered by ultrafast spin–phonon interactions

“…We first measure the transient mean strain of the NiO layer using ultrafast reciprocal space mapping (URSM, see details in Methods and Refs. 36 , 37 ). Figure 4b presents the out-of-plane strain (gray dots) derived from time-resolved reciprocal space maps (see Supplementary Note 8 ) around the reflection peak of a NiO (25 nm)/Pt(2 nm) thin film.…”

“…URSM experiments 36 are conducted with hard X-ray probe pulses at 8 keV, which are derived from a laser-driven X-ray plasma source 37 and have a duration of approximately 200 fs and a footprint of about 300 µm. A more than three times larger area of the Pt layer is excited by p -polarized pump pulses with a duration of 100 fs at a central wavelength of 800 nm, which are incident under 25° relative to the surface normal with a fluence of 10 mJ/cm 2 .…”

Phonon‐Dominated Energy Transport in Purely Metallic Heterostructures

“…[20,21] The shifts of the material-specific Bragg reflections in reciprocal space were converted to a time-dependent average lattice strain for each layer. [22] The experimental results for the samples S1-S4 at a common incident pump fluence of ≈10 mJ cm −2 are gathered in Figure 1. The transient strain evolution in Ni and Au (Figure 1b,c) consists of a superposition of coherent longitudinal acoustic phonon wavepackets and incoherent contributions (thermal expansion).…”

Phonon-dominated energy transport in purely metallic heterostructures

“…We use ultrashort x-ray pulses generated by a table-top laser-driven plasma x-ray source (PXS) to record transient angular shifts of Au (111) and Ni (002) Bragg reflections after excitation of the sample with an ultrashort 800 nm laser pulse 19,20 . The shifts of the material-specific Bragg reflections in reciprocal space are converted to a time-dependent average lattice strain for each layer 21 . The experimental results for the samples S1-S4 at a common incident pump fluence of approx.…”